ON THE CHEMICAL PROPERTIES OF SILK. 153 



Nitric acid has a strong influence upon silk ; and, 

 if mixed with alcohol, changes silk to a permanent 

 bright golden yellow colour. The same acid, when 

 concentrated and distilled off silk, yields by evapo- 

 ration oxalic acid ; and if the evaporation is still 

 farther continued, the same acid, together with a 

 quantity of yellow octohedron-sided truncated crys- 

 tals are obtained. These are free from an acid 

 taste, but of a strong bitter, and if applied to the 

 skin leaves a deep yellow stain. When the re- 

 maining liquor is saturated with potash, and eva- 

 porated, the residue is a rather yellow salt, which 

 detonates when placed on live coals, like nitre. 

 Chemists suppose this to be a treble combination of 

 the bitter principle above mentioned, together with 

 nitrate of potash. 



Silk is dissolved and corroded by the caustic 

 alkalis ; and chlorine renders it yellow, It 

 yields a greater quantity of volatile alkali than 

 almost any other substance. It was found by 

 Tournefort to contain even more than hartshorn, as 



obtained from fifteen ounces of silk two drachms 



volatile salt. This preparation was at one 

 time in high repute in England as a medicine ; 

 and was called English Drops, or " Guttse Angli- 

 canse." The cocoons of silk were reduced into a 

 powder by Pomet, and used as a medicine. In his 

 History of Drugs he says, that silk thus prepared had 



VOL. III. L 



